In refractory castables, ramming mixes and pressed bricks, lignosulfonate is used as a temporary (organic) binder. It gives the unfired material green and dry strength so that it can be shaped, handled and installed; during heat-up the organic binder burns out and the permanent ceramic bond forms by sintering at high temperature. Lignosulfonate can also act as a dispersant that lowers the water demand of fine refractory powders.
Where Lignosulfonate Is Used in Refractories
| Product type | Function of lignosulfonate | What to watch |
|---|---|---|
| Pressed bricks (e.g. magnesia, fireclay, alumina) | Temporary binder for green and dry strength before firing | Even distribution; moisture of the press mix |
| Ramming and gunning mixes | Binder giving workability and strength after placement and drying | Strength in the drying range, before the ceramic bond forms |
| Castables | Dispersant for fines (lower water demand) and supplementary organic binder | Interaction with cement and other deflocculants; setting time |
| Plastic refractories and mortars | Binder and plasticity aid | Shelf life; drying shrinkage |
How the Temporary Bond Works
- Mixing: lignosulfonate dissolves in the mixing water and coats the grains.
- Drying: as water evaporates, lignosulfonate forms solid bridges between grains, giving dry strength.
- Heating: the organic binder decomposes and burns out at relatively low temperature; the material passes through a zone of lower strength.
- Firing / service: the permanent bond forms by sintering or by the hydraulic or chemical bond of the system. Patent literature on magnesia bricks, for example, describes sulfite lye as a temporary bonding agent with the ceramic bond forming only on firing above about 1200 °C.
Choosing a Grade
| Requirement | Grade direction | Reason |
|---|---|---|
| Low impurity contribution to the fired product | Low-ash, low-insoluble sodium or magnesium grade | Ash and cation remain after burnout |
| Avoid sodium in high-alumina or basic refractories | Calcium or magnesium lignosulfonate | Sodium can form low-melting phases |
| Maximum green strength | Binder-grade, higher-molecular-weight lignosulfonate | Larger molecules form stronger bridges |
| Lower water demand in castables | Dispersant-grade lignosulfonate or a naphthalene sulfonate | Better deflocculation of fines |
| Parameter (TDS) | Magnesium lignosulfonate GAC-MgLS-1 | Calcium lignosulfonate GAC-CaLS-1 |
|---|---|---|
| Lignosulphonate content | 55% min (dry basis) | 55% min (dry basis) |
| Dry matter | 95% min | 95% min |
| Water-insoluble matter | 1.0% max | 1.5% max |
| Moisture | 5% max | 5% max |
| pH | 4–7 | — |
Trial Procedure
- Make test pieces with 2–3 binder levels and a control.
- Measure green and dry cold crushing strength (CCS) and bulk density.
- Measure strength after heat treatment at intermediate temperatures, where the organic binder has burnt out but sintering is incomplete.
- Check fired properties (CCS, porosity, permanent linear change) to confirm the binder has no negative effect.
- Record mixing water, pressing pressure and drying schedule.
Frequently Asked Questions
Why is lignosulfonate called a temporary binder in refractories?
Because it gives strength only before firing. It burns out during heat-up and the permanent ceramic bond forms at high temperature.
Does lignosulfonate leave residue in fired refractories?
The organic part burns out, but the cation and inorganic ash remain. Low-ash grades and a suitable cation keep this contribution small.
Which lignosulfonate is preferred for magnesia bricks?
Calcium or magnesium lignosulfonate is often preferred over sodium grades to avoid adding sodium. Confirm with green-strength and fired-property tests.
Related Pages
- Magnesium lignosulfonate
- Calcium lignosulfonate
- Sodium lignosulfonate binder grade
- Lignosulfonate as a metal powder binder
Questions about a specification, a test method or a trial: contact us or email info@greenagrochem.com.
